This invention relates to ophthalmoscopes and ophthalmoscopic cameras, and more particularly to improvements of an objective lens for use in such ophthalmoscope or ophthalmoscopic camera.
Most of the ophthalmoscopic cameras which have found wide acceptance are designed to have an objective lens comprised of a positive meniscus lens convex toward an eye to be examined with limitation of its view angle to about 30 degrees. To increase the image angle up to about 45 degrees, it is known to make use of a biconvex lens as the objective lens. It has also been proposed by the present applicant to construct the objective lens from a positive meniscus lens concave toward an eye to be examined and a positive meniscus lens concave toward an image thereof as described in U.S. Pat. No. 3,914,032.
With the objective lens having an increased view angle, it is desired to reduce astigmatism. Incorporation of an apertured mirror as arranged between the objective lens and an image forming lens to reflect the illuminating light rays from a light source in the direction of the optical axis of the eye leads to a further requirement of increasing the relative aperture of the objective lens, while still minimizing spherical aberration and coma thereof. As the objective lens is positioned in the path of the illuminating light rays, there is some possibility of producing disturbing light reflection due to the light rays reflected from the surfaces of the objective lens to the film plane.